1. Field of the Invention
The present invention relates to a vertical alignment liquid crystal display that is driven by multiplex driving.
2. Description of the Related Art
A liquid crystal display is widely used, for example, as an information display unit in various electronic devices for consumer use and automobile use. A general liquid crystal display is configured by disposing a liquid crystal layer made of a liquid crystal material between two substrates disposed facing each other by providing a gap of about several nm therebetween. As one type of liquid crystal display described above, known is a vertical alignment liquid crystal display (for example, JP-A-2005-234254). A vertical alignment liquid crystal display comprises, as its main configuration, liquid crystal cells of a vertical alignment mode in which liquid crystal molecules in a liquid crystal layer disposed between two substrates are aligned substantially vertically relative to the surface of the respective substrates, and polarizers provided respectively to the outer side of these liquid crystal cells. The respective polarizers are often of a crossed Nicol arrangement. As a result of adopting this configuration, the transmittance of the liquid crystal display during the non-application of voltage will become extremely low and, therefore, a high contrast can be realized relatively easily.
When realizing the display of images of a liquid crystal display based on multiplex driving, for example, substrates having electrodes which are respectively formed in a stripe shape are disposed to face each other so that the extending directions of the respective electrodes are substantially orthogonal, and each region where the electrode of one substrate and the electrode of the substrate intersect is used as a pixel. Here, the shape of each pixel is substantially rectangular. Moreover, alignment treatment such as rubbing treatment is performed to the surface of the respective substrates. The direction of performing the alignment treatment to the surface of the respective substrates is set, for example, to opposite directions (anti-parallel alignment). Consequently, the alignment direction of the liquid crystal molecules of the liquid crystal layer provided between the substrates at the substantial center in the layer thickness direction during the non-application of voltage will orient a single direction. For example, when the direction of the alignment treatment performed to the respective substrates is set to a 6 o'clock direction and a 12 o'clock direction when viewed from a front view of the liquid crystal display, the alignment direction of the liquid crystal molecules at the substantial center of the liquid crystal layer in the layer thickness direction will orient in the 6 o'clock direction. Here, the extending direction of the electrode of one side substrate becomes substantially parallel to the alignment direction of the liquid crystal molecules at the substantial center of the liquid crystal layer in the layer thickness direction, and the extending direction of the electrode of the other substrate becomes substantially orthogonal. Moreover, the initial alignment state of the liquid crystal layer may be a twisted alignment state.
In a liquid crystal display of the foregoing vertical alignment mode, considered may be a case where a pair of polarizers in a substantial crossed Nicol arrangement is disposed at the outer side of the respective substrates. Let it be assumed that an absorption axis of one polarizer is disposed at an angle of approximately 45° relative to the direction of the alignment treatment performed to one side substrate. When forming a liquid crystal layer using a liquid crystal material having negative dielectric constant anisotropy and applying voltage of a threshold voltage or higher between the electrodes of the respective substrates, most of the liquid crystal molecules in the liquid crystal layer will tilt to a horizontal alignment direction according to the alignment treatment direction. When observing this liquid crystal display, a light display state is favorably observed from the 6 o'clock direction, but contrarily a light display state cannot be observed from the 12 o'clock direction. Here, the 6 o'clock direction is referred to as an optimal viewing direction (optimal viewing orientation), and the 12 o'clock direction is referred to as an anti-viewing direction (anti-viewing orientation).
In a liquid crystal display of the foregoing vertical alignment mode, when the liquid crystal display is viewed from the anti-viewing direction in a state where the liquid crystal display is of a light display state from a front view, the inside of the pixels will be observed as a substantially dark state, but a light leak will occur near one side among the four sides (pixel edges) of a rectangular pixel. This light leak is non-uniformity in its developmental state and differs by pixel, and considerably drops the display quality in terms of appearance.
Moreover, in a liquid crystal display of the foregoing vertical alignment mode, there are cases where a dark region occurs in the respective pixels in a state where the liquid crystal display is of a light display state from a front view during multiplex driving, thereby causing the display quality to drop. Since this phenomenon occurs more notably when the frame frequency is decreased, the drive frequency needs to be set higher in order to eliminate this phenomenon. Nevertheless, when the drive frequency is increased, the consumption current increases as a result of the impedance between the electrodes increasing, and, in addition to the load of the drive device increasing, the potential difference of the electrodes also becomes notable, causing the display quality to drop. Specifically, this increases the potential of so-called cross-talk.